Process for decorating sheet material



March 31, 1942. R, BQICE 2,278,056

PROCESS FOR DECORATING SHEET" MATERIAL Filed Aug. 30, 1939 I .RZLJIGZZ .BOiOG INVENTOR" M ATTOIRNEY Patented Mar. 31, 1942 PROCESS FOR DECORATING SHEET MATERIAL Russell Boicc, Newburgh, N. Y., assignor to E. I.

du Pont de Neinours & Company, Wilmington, Del., a corporation of Delaware Application August 30, 1939, Serial No. 292,560

3 Claims.

This invention relates to machines for coating flexible sheet material and more particularly to improved equipment for applying finish coats of cellulose derivative compositions to fl xible sheet; material.

In conventional coating machines the sheet to be coated is passed over suitable transverse rollers and below a doctor knife disposed between the said rollers. An excess of the coating composition is supplied in front of the doctor knife where it is spread on the sheet in the form of a continuous uniform film.

It has previously been proposed to use doctor rollers instead of the doctor knife for the application of the coating composition in which case the doctor roller is driven in the direction of movement of the sheet being coated. It has also been proposed to drive the doctor roller in the opposite direction of movement of the sheet being coated. Further, it has been proposed to drive the doctor roller at a speed different from the rate of movement of the sheet passing under the doctor roller. i

The conventional doctor knife is satisfactory for spreading the basecoats on a sheet but is not altogether satisfactory for applying the final finishing coats since any insoluble particle or foreign matter which collects under the knife causes streaks or scratches in the finished product. Further, in the case of doctor knife coating any unevenness in the surface being coated 7 causes an uneven amount of the finishing coat to be deposited and hence a variation in finish is obtained which is very objectionable. Still further, the doctor knife is not suitable for applying a final protective coat to a variegated surface such as printed or stenciled material. When the variegated surface passes under the doctor knife, there is a slight drag of the coating composition which has a solvent action on the base material, and the various colors are streaked or smeared as a result of the said dragging action.

Some of the disadvantages of the doctor knife for applying finishing coats to flexible sheets are overcome to a certain extent by the use of a driven doctor roller.

is the case when a finish of contrasting color to the base material or when a dull finishing com The .driven doctor rollers, however, are objectionable since they do notv deposit a uniform film on a smooth surface. As-

This invention has as an object the provision of an apparatus to apply finishing coats to a flexible sheet material which overcomes the disadvantages of the prior art apparatus.

A further object is the provision of an apparatus the use of which insures an exceptionally uniform application of a finish coat by means of one or more undriven rotatable doctor rollers.

A still further object is the provision of coating equipment which insures the absence of a mottled appearance in the finished product.

Other objects will appear as the description of the invention proceeds.

These objects are accomplished by means of an improved coating head which comprises an undriven rotatable doctor roller to apply or spread the coating composition in the form of a film and a smaller auxiliary undriven rotatable doctor roller located immediately behind the larger primary doctor roller to smooth or trowel the film spread by the first doctor roller, the two doctor rollers operating in conjunction with an endless belt which carries the sheet to be coated under the said doctor rollers.

In the drawing Figure 1 is a sectional elevation of the coating head with the various parts arranged according to the present invention as will be apparent as the description proceeds. In Figure 1, l0 and I2 represent two rotatable rolls around which an endless belt 9 is placed. This belt supports the fabric to be coated shown as 8; Located above the belt and fabric are two doctor rollers 2 and 3. The former is -a primary undriven doctor roller andv the latter is an auxiliary undriven doctor roller. The material used in coatingthe fabric, such as nitrocellulose jelly, is shown as l3. Another vertical adjusting roller indicated as H is located beneath the two doctor rollers over which the endlessbelt .passes. This roll is adjustable vertically to increase the tension on the endless belt 9. Ears (not shown) may be placed at the ends of the doctor rollers 2 and 3 to prevent the coating composition from running over the edge. I 1

Figure 2 is a plan view of roller 2 showing cutouts 4. This figure likewise would represent roller 3 where the cut-outs are pasted onto this roller instead of roller 2. Where they are pasted to roller 2, roller 3 is eliminated.

In the operation of the apparatus according to the present invention, the flexible sheet material 8 is unwound from the unwind (not shown) and passed over tension rollers (not shown) to the endless rubber blanket 9, which carries the sheet material 8 under the doctor rolls 2 and 3 and into any suitable type of drying apparatus. The endless rubber blanket is mounted on two rollers l and 12. The first roller I0 is adjustable horizontally to regulate the tension of the endless blanket, the second roller I2 is located at a suitable distance from the first roller, usually about 14 to 16 inches in the same horizontal plane as roller 10. The roller I2 is driven by any suitable mechanism. Between rollers l0 and I2, and behind doctor rollers 2 and 3 there is located a vertical adjusting roller to further regulate the tension of the rubber blanket, as well as regulating the direction of travel of the sheet material after passing under roller 3. The doctor rollers 2 and 3 are mounted in bearings and are rotated by the material passing under the rollers, which is pressed againstv the rollers by the endless rubber blanket 9.

The coating composition, such as a cellulose derivative composition dispersed in organic solvents, is delivered on the sheet 8 immediately in front of the undriven rotatable doctor roller 2. The doctor roller 2 spreads an uneven film of the coating composition on the sheet material 8, which would. have a streaky, mottled appearance if it were not for the action of roller 3. I The roller 3 has a wiping or smoothing action, similar to a troweling action, which tends to reduce the size of the streaks and prevent the mottled appearance. The streaky, mottled effect is very pronounced or accentuated when a cellulose derivative finishing coat having a color or lustre contrastin to the base material is applied to an unembossed or slightly embossed cellulose derivative coated fabric which has a relatively smooth surface.

It is very important that the second roller 3 be smaller than the first roller 2 since the size of the streaks in the deposited film after drying is in direct proportion to the size of the second roller 3. In the preferred embodiment of this invention the diameter of the primary doctor roller 2 is 1% inches and the diameter of the auxiliary wiper doctor roller 3 is 1 /4 inches and the horizontal distance between the axes of the two rollers 2 and 3 is two inches. Since the size of the firstroller 2 controls the amount of coating composition applied to the material being coated, it is not practical to use a doctor roller which is appreciably less than 1 inches in diameter. The horizontal distance between the peripheries of the two rollers is 1 of an inch. When the roll of coating composition l3 in front of roller 3 reaches a certain size, the composition contacts roller 2 and is carried backto the roll of coating composition l3 in front of roller 2.

With respect to the auxiliary roller it may be less than the preferred dimension which is 1% inches in diameter. The smaller the-second roller. the smaller the streaks in the coating composition applied. However, the second roller should have a diameter which is greater than the height of the roll of coating composition which collects in front of the second roller. If the diameter of the second roller is less than the height of the roll of coating composition which collects in front of the second roller, the coating composition will flow over the roller and damage the sheet material being coated.

- For practical purposes the size of the streaks or mottled appearance resulting from the use of an auxiliary roller 1 inches in diameter is not objectionable since the streaky mottled effect re- "i sulting from a roller this size is not visible to the casual observer. However, a wiper, roller or smoothing roller which is appreciably greater than 1%; inches in diameter produces a streakymottled effect in the coating which is able.

After passing under the two undriveegi doctor bjectionrollers 2 and 3, the material being coat d enters a heating chamber where the solvents re volatilized and recovered. The'heating cham Where the streaky mottled effect is n t objectionable, the smoothing or wiping docto roller may be eliminated entirely. It is also p0 sible to obtain special decorative effects with the use of only one undriven doctor roller, in which case conventional masking tape cut out in the form The cut-outs are approximately .012 inch thick;

however, other thicknesses may be used, such as, e. g.. .005 to .020 inch. The invention is not to be limited by specifically mentioning this range since other thicknesses of cut-outs may be used, depending upon the viscosity and type of decorating compositions employed. It is to be understood that such cut-outs may be applied to the second roller 3, in which case both rollers are used, or to the first roller 2', in which case the second roller 3 is eliminated.

At the edges of the cut-outs adhered to the doctor roller there is collected an excess of the coating composition which deposits the excess onto the sheet material 8 as it passes under the doctor roller. In this manner the outline of the cut-outs is transferred to the sheet material. In this case the coating composition used in the last two passes is of a contrasting color or lustre to the first coat. The design which is in relief on the undriven doctor roller will be outlined on the sheet material being decorated. The conventional masking tape used for finishing automobiles is desirable due to its low cost and the ease with which it may be readily attached and detached.

It is also possible to employ the double roller coating device above described with a conventional horizontal coating head without the aid of the rubber blanket. In this modification the two undriven rotatable doctor rollers are located between two transverse rollers in the same plane. The sheet material to be coated passes over the first transverse roller and under the two undriven rotatable doctor rollers and over the second transverse roller. In this case two doctor rollers push down on the sheet material with sufficient-pressure that the sheet material passing under the undriven doctor rollers will rotate the said doctor rollers. Since no supporting element is required for the sheet material being decorated, as it passes under the doctor rollers, the pressure applied is insufficient to alter the sheet material being coated in order that it will be sufliciently taut to rotate the undriven doctor rollers.

While I have illustrated the invention by examples in which cellulose derivative coated fabrics have been decorated. it will be apparent that other coated fabrics may be treated in like manner; for example, those having a base coat of rubber, resins, synthetic or natural, either alone or in combination with rubber and cellulose derivatives, and other synthetic polymers such as those known as nylon. In any case the surface coat should preferably be of a color contrasting to the base coat so that the design imparted by the cut-outs will stand out prominently.

The apparatus disclosed has been found to be I completely effective in the prevention of the objectionable mottled surface appearance in pyroxylin coated fabrics. The present invention reduces production cost since it makes possible the application of the same amount of coating composition in a uniform film with one pass through the coating machine, which previously required two passes. Another advantage of the apparatus of this invention is that it provides a means for finishing variegated pyroxylin surfaces without smearing or streaking the separate colors. A still further advantage of the present invention is that there is provided a means for applying a uniform surface film on an embossed surface. Prior art.

expedlents, such as doctor knife application of a finishing coat to an embossed surface deposited the coating composition in the valleys of the grain and scraped the tops clean of the finishing composition.

This application is a continuation-in-part-of my co-pending application, Serial No. 203,256, filed April 21, 1938, now U. S. Patent 2,196,894.

It is apparent that many widely different embodiments of this invention may be made without departing from the spirit and scope thereof; and, therefore, it is not intended to be limited except as indicated in the appended claims.

I claim:

1. A process for decorating a coated sheet which comprises passing the coated side of said sheet under and against a doctor roller having a design in relief thereon, causing said roller' to be pushed down on said sheet with suilicient pressure whereby said roller is rotated by the movement of said sheet, the amount of pressure being insuflicient to alter the contour of said sheet, applying a coating composition in the form of a jelly of contrasting color to said sheet before contact with said roller in such a manner that a roll of said coating composition of less height than said roller is collected in front of said roller, whereby in passing under and against said roller a greater amount of said composition is retained on said sheet'where it contacts the edges of'the raised portion of said roller than elsewhere on said sheet, and drying the coated sheet. 2. Aprocess of decorating a cellulose derivative coated sheet which comprises passing the coated side of said sheet under and against a doctor roller having a design in relief thereon, causing said roller to be pushed down on said sheet with suflicient pressure whereby said roller is rotated by the movement of said sheet, the amount of pressure being insumcient to alter the contour of said sheet, applying a cellulose derivative coating composition in the form of a jelly of contrasting color to said sheet before contact with said roller in such a manner that a roll of said coating composition-of less height than said roller is collected in front of said roller, whereby in passing under and against said roller a greater amount of said composition is retained on said sheet where it contacts the edges of the raised portion of said roller than elsewhere on said sheet, and drying the coated sheet. v 3. A process for decorating a coated sheet which comprises passing the coatedside of said sheet under and against a plurality of rotatable doctor rollers, causing said rollers to be pushed down on said sheet with suflicient pressure whereby said rollers are rotated by the movement of said sheet, the last doctor roller having a design in relief thereon, the amount of pressure being insuflicient to alter the contour of said sheet, applying a coating composition in the form of a Jelly of contrasting color to said sheet before contact with said rollers in such a front of said last roller, whereby in passing under and against said last roller a greater amount of said composition is retained on said sheet where it contacts the edges of the raised portion of said last roller than elsewhere on said sheet, and drying the coated sheet.

RUSSELL BOICE. 

